Recently, instances are increased where an LED (Light-Emitting Diode) is used as a light source across the entire industrial field including the lighting devices, and as a result, researches are also briskly waged in every industrial field in order to efficiently and effectively use the LED.
A light generated from an LED has a characteristic where a light distribution is concentrated on a central area over a surrounding, and therefore, the light is not evenly distributed to the surrounding area, and a front surface area of LED becomes disadvantageously brighter and the light is gradually darkened as distanced from the front area of LED.
In order to solve the abovementioned disadvantages, demands on technologies to evenly diffuse a light generated from an LED are on the increase.
Meantime, although it is necessary to diffuse a light emitted from an LED evenly and symmetrically, it is also necessary to diffuse the light only to a particular direction more profusely depending on arrangement of LED. For example, when a horizontally gapped arrangement of LED is denser than a vertically gapped arrangement of LED, an entire even distribution of light can be obtained when the light is more diffused to a vertical direction while the light is less diffused to a horizontal direction.
Referring to the conventional light diffusion lens (50) may include a semi-spherical body, an equiaxed upper surface (54), a plane surfaced lower surface (56) and an equiaxed lateral surface (58) perpendicular to the lower surface (56).
The lower surface (56) may be disposed at a center with an incident port (not shown) accommodated by an LED (not shown). Furthermore, an incident surface (60) may be formed that is convexly recessed from the incident port to a direction of the upper surface (54). Each of the upper surface (54) and the incident surface (60) may have a predetermined curvature.
FIG. 2 is a schematic view illustrating a light diffusion operation of a light diffusion lens according to the prior art as shown in FIG. 1.
FIG. 2 is a schematic view illustrating a light refraction state inside a light diffusion lens according to the prior art.
Referring to FIG. 2, a light emitted from an LED may be introduced into the body (52) through the incident surface (60), and emitted to outside through the upper surface (54).
The body (52) may be formed with a glass or a plastic material. Thus, the body (52) may be higher in density than the air and also higher in refractive index.
The light emitted from the LED may be introduced into the body (52) through the incident surface (60), and initially refracted, emitted from the body (52) through the upper surface (54) and refracted second time.
The light emitted from the LED may be emitted through a path more bent to a surrounding direction than an original path due to density difference between the air and the body (52). That is, the light emitted from the LED is diffused to a surrounding area.
The light reflected again from the lower surface (56) after being bent from the upper surface (54) to the lower surface (56) in FIG. 2 is caused by an inner reflection. It can be ascertained from FIG. 2 that the light distribution state by a single light diffusion lens shows that there is a bright area in the center.
According to FIG. 2, a BLU (Back Light Unit), wherein a light distribution made by each light diffusion lens is respectively arranged in series, is alternated with a dark area and a bright area, and as a result, it can be ascertained therefrom that the quality of BLU set is deteriorated.
FIG. 3 is a schematic view illustrating a light distribution state obtained by a light diffusion lens of FIG. 1 according to the prior art.
Referring to FIG. 3, it can be ascertained that the light distribution forms a rotating symmetrical shape, which is due to the fact that the light diffusion lens (50) illustrated in FIG. 1 has a rotating symmetrical light distribution characteristic.
Referring to FIG. 3 again, it can be noted from FIG. 3 that there are areas darker than surrounding areas, and there are areas brighter than surrounding areas. A particularly bright area in the center among the bright areas is called a hot spot, and a dark area around the hot spot is called a dark portion (darkness).
The brightness contrast between the hot spot and the dark portion is so great as to be a cause of hindering an even light distribution. Thus, demands are required to maximally mitigate the hot spot and the dark portion generated from a light diffusion lens.
The hot spot and the dark portion are known to be generated from limit of diffusion and total reflection within a light diffusion lens, that is, a light on a central area among lights emitted from an LED not being fully diffused to a surrounding area.
FIG. 4 is a schematic view illustrating a strength distribution of light diffused by a light diffusion lens of FIG. 1.
The vertical axis in FIG. 4 shows a distance from an optical axis (unit: mm) and a horizontal axis shows an optical strength (unit: Lux).
Referring to FIG. 4, it can be noted from FIG. 4 that an area where an optical strength reaches a peak at a central area becomes a hot spot and an area where the optical strength is greatly decreased becomes a dark portion. Furthermore, it can be also ascertained from FIG. 4 that an optical strength distribution is abruptly uneven between the hot spot and the dark portion while the optical strength distribution is relatively smooth and evenly distributed between the dark portion and an edge.
FIG. 5 is a schematic view illustrating a light diffusion device where several light diffusion lenses of FIG. 1 are arranged to a crosswise direction.
The light diffusion device (70) illustrated in FIG. 5 needs adjustment of light distribution of each light diffusion lens because a plurality of light diffusion lenses is adjacently disposed.